1. Field of the Invention
The invention relates to a stencil printing machine of the type capable of preparing a stencil from a continuous roll of stencil sheet, said stencil being cut to a dimension according to a selected size of printing paper, attaching the aforesaid stencil to a printing drum, and printing the stencil image onto the printing paper. When the need to print from a new stencil arises, the printing machine is further capable of removing the used stencil from the aforesaid printing drum and transporting the used stencil to a container by means of a stencil removal mechanism.
2. Background
Conventional stencil printing machines, specifically those types that make use of a printing drum capable of accommodating paper sizes up to A3, are normally able to print on paper sizes smaller than A3. In cases where paper sizes smaller than A3 are printed, an A3 size stencil must still be cut off of the roll of stencil sheet and attached to the printing drum. When this type of printing machine is used to print a relatively small number of copies, the cost of the stencil can become the largest expense per sheet printed.
In order to reduce stencil expenses, a stencil making apparatus has been put forth wherein multiple separate printing drums having A3, B4, A4 and/or other size printing surfaces are utilized, these printing drums being of a replaceable design so as to allow the use of a specific drum corresponding to the size of the paper intended for the printing job. A structure is generally utilized whereby the aforesaid printing drums are constructed to a uniform diameter, and their ink-permeable printing regions disposed so as to begin at a common baseline where an adjacent clamp mechanism is provided, but to end at a location corresponding to the length of the paper size for which the drum was intended.
Moreover, a stencil printing machine has been proposed wherein a single printing drum is used to accommodate the mounting of various size stencils cut to conform to A3, B4, A4, and/or other dimensions. In cases where B4 or A4 size stencils are wound around the drum, the drum surface printing region lying beyond the end of the stencil is exposed, thus making it necessary to provide a control mechanism to prevent the press roller from pressing the region of the drum surface not covered by the stencil.
In the stencil making printing machines discussed above, a stencil is unwound and prepared from a continuous roll of stencil sheet and cut to a dimension according to a selected size of printing paper before wound around the drum, and thus more economical use of the stencil sheet is made, whereby printing costs can be reduced.
Current stencil printing machines generally provide means of removing the used stencil from the aforesaid printing drum, and removal rollers as means of transporting the used stencil to a used stencil container when a new stencil is to be prepared. The used stencil cannot be deposited completely into the used stencil container unless the rotational duration of the removal rollers exceeds a linear distance equivalent to the length of the stencil being removed from the drum. The rotational duration of the removal rollers is thus generally established, while also taking the length of the stencil removal traverse path into consideration, so as to slightly exceed a linear distance equivalent to the length of the largest usable stencil which is, in many cases, an A3 size stencil.
In cases where a stencil smaller than the largest permissible stencil is mounted to the drum, the removal rollers continue to rotate after the used stencil is completely deposited in the used stencil container, thus posing a potential problem whereby used stencils already transported and placed into the container may become entangled in the turning removal rollers after the most recent used stencil has been deposited.
The invention, in consideration of the aforesaid used stencil entanglement problem, offers a structure for a stencil printing machine of the type capable of cutting a stencil from a roll of stencil sheet to a length corresponding to the length of the printing paper, attaching the aforesaid stencil to the circumference of a drum, removing the stencil from said drum when a new stencil is to be prepared, and transporting said stencil to a used stencil container by means of a transport mechanism; wherein operation of the aforesaid stencil transport mechanism is specifically controlled so as to stop traverse of the used stencil at a point immediately after said stencil is completely deposited in the aforesaid used stencil container.
The invention, as means of realizing the aforesaid operation, offers a structure for a stencil printing machine of the type capable of cutting a stencil from a roll of stencil sheet to a length corresponding to a selected size of printing paper, attaching the aforesaid stencil to the circumference of a drum, detaching the stencil from said drum when a new stencil is to be attached, and transporting said stencil to a used stencil container by means of a stencil removal transport mechanism; wherein a stencil length specifying means is provided to determine the length of the stencil according to the monitored length of the printing paper selected for that specific printing job, and a control means is provided to control operation of the aforesaid transport mechanism in relation to the length of the stencil when said stencil is removed. The length of the aforesaid stencil is established as the length of that stencil when attached and extending around the external circumference of the aforesaid drum.
The aforesaid control means may be comprised of memory means that holds stencil length data in memory as specified by the aforesaid stencil length specifying means, monitoring means that determines the minimum extent of transport needed to completely carry each of various size stencils to and into the aforesaid used stencil container by the aforesaid transport means, and termination means that stops the operation of the aforesaid transport means based on a comparison calculation of the length of the aforesaid stencil monitored by the aforesaid monitoring means and the stencil length data held in memory by the aforesaid memory means.
While an ordinary positional relationship is maintained between the drum and the used stencil container, the stencil is normally completely inserted into the used stencil container within the time required for one revolution of the drum, thus establishing a direct correlation between the stencil removal process and the revolving angle of the drum. It thus becomes desirable to structure the aforesaid monitoring means so as to monitor a rotational angle of the drum as means of establishing a specific traverse distance of the aforesaid transport means, said traverse distance being equal to the minimum distance required to deposit a specific size stencil into the used stencil container.
The aforesaid monitoring means may be comprised of a first trigger plate fixedly attached to the radial peripheral edge of the drum, a separate trigger plate fixedly attached to the peripheral edge of the drum at a point of specific rotational angle spaced from the aforesaid first sensor plate in a direction opposite to the drum rotating direction, and a stationary sensor capable of detecting the aforesaid first and separate trigger plates. The first trigger plate is advantageously positioned at a location at which it can trigger the aforesaid stationary sensor at the point where the printing drum begins its rotation movement upon removal of the used-stencil from the drum.
The aforesaid monitoring means may also be structured in the form of a rotational angle reading encoder, or other like means, capable of continuously monitoring the rotational position of the drum whereby an angle of drum rotation can be applied to the establishment of the aforesaid specific traverse distance of the transport mechanism.
A further purpose of the invention is to provide means of controlling operation of the transport means without employing the aforesaid stencil length specifying means. In other words, the invention offers a structure for a stencil making printing machine of the type capable of cutting a stencil from a roll of stencil sheet to a length corresponding to the length of the printing paper, attaching the aforesaid stencil to the circumference of a printing drum, detaching the stencil from said drum, and providing means to transport said stencil to a used stencil container; wherein a removal sensor is provided in proximity to the aforesaid used stencil container as means of monitoring the passage of a used stencil, said sensor being applied in a way in which the operation of the aforesaid transport mechanism can be stopped in relation to the passage of the aforesaid used stencil.